The present invention relates to an electronic piano or similar electronic musical instrument having a capability of effecting vibratos with a desired tone which is produced by pressing down a key provided on a keyboard.
An electronic musical instrument such as an electronic piano has heretofore been proposed in various forms, as disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 48-34523 by way of example. A prior art instrument of this kind includes a keyboard, a key detector for detecting a key on the keyboard 12 which is pressed down, a key constant memory loaded with key constants each being associated with a different tone which may be produced by pressing a particular key, an address signal generator for generating an address signal by effecting an arithmetic operation with any of the key constants at a predetermined period, a tone waveform memory storing the amplitudes of a tone waveform associated with various sampling points in the form of digital values, a digital-to-analog (DA) converter for sequentially converting into analog values the digital amplitudes which are associated with the individual sampling points and read out of the tone waveform memory to thereby produce a tone signal. Various approaches have also been proposed for providing such an instrument with a vibrato effecting capability, as shown and described in Japanese Patent Publication No. 57-22399, for example. Specifically, to effect vibratos with a certain tone, the frequency f of the tone is oscillated up and down. Concerning a tone C.sub.4, for example, the frequency f of 261.626 hertz may be repetitively varied over a range of .+-.10 hertz once per a specific period such as 5 hertz. The range of .+-.10 hertz may be increased to render the vibrato stronger or decreased to render it weaker. For the same width of .+-.10 hertz, the vibrato effect achievable differs from, for example, the vibrato frequency of about 5 hertz to the vibrator frequency of about 10 hertz. Assuming the tone C.sub.4 whose frequency is 261.626 hertz and the vibrato frequency of 5 hertz, a vibrato effect is achievable by sequentially varying the frequency as 261.626 hertz, 271.626 hertz, 261.626 hertz, 251.626 hertz, 261.626 hertz and so forth. Then, a different vibrator effect will be produced if the vibrato frequency is changed from 5 hertz to 10 hertz with the transitions of frequency of the tone C.sub.4 being maintained the same. In this manner, the vibrato effect for a given tone depends on the width over which the frequency of the tone is increased and decreased once from the center frequency and, also, on the vibrato frequency. More specifically, when a certain key on the keyboard is pressed down, a tone associated with the key has its center frequency increased and decreased over a predetermined frequency width during a predetermined period thereof.
The prior art instrument described above is provided a multiplier for multiplying an output signal of the key constant memory and a control signal fed from a vibrato controller. The rate of generating address signals for reading the amplitudes associated with the individual sampling points out of the tone waveform memory, i.e., the output timing is controlled on the basis of the output of the multiplier.
A drawback with such an instrument heretofore proposed is that the multiplier and vibrato controller are extremely complicated in construction. Furthermore, when the instrument is controlled by a computer, not only a substantial period of time is needed for the processing but also a microprocessor of the computer has to bear an extra load.